It's cop talk. The current US DEA emerged from the "Bureau of Narcotics and Dangerous Drugs" which came from the "Federal Bureau of Narcotics" which came from the "Federal Narcotics Control Board" established by the "Narcotics Tax Act" in 1914, back when Prohibition was a thing and they were worried about opium. Law enforcement culture has thus gone off into the weird by themselves, and they use "narcotic" to mean "any forbidden substance".
